Is Emergency Departments (ED) Syndromic Surveillance
Useful for Monitoring General Illness Trends?
L EDWARDS, A WILDER,
A BERGMANN, J SCALETTA,
J CASANI, D BLYTHE
Office of Epidemiology and Disease Control Programs, Maryland Department of
Health and Mental Hygiene
Background: ED syndromic surveillance systems
that classify ED clinical data into syndrome categories may help
identify unannounced bioterrorist attacks. They may also provide
insight into overall disease patterns in the community, although
this has not been clearly demonstrated previously.
Methods: Beginning September 12, 2001, ED logs
from nine Maryland hospitals were coded daily into eight illness
categories – death, sepsis, rash illness, respiratory illness,
gastroenteritis, unspecified infection-like illness (UI), neurological
illness, and all other visits. The average weekly proportion of
ED visits coded as respiratory was compared to the weekly number
of respiratory outbreaks reported to the state health department.
Kappa statistics were calculated correlating weeks when the average
proportion of respiratory ED visits increased by > 10% to weeks
when reported respiratory outbreaks increased by two or more.
Results: The percentage ED visits coded as respiratory
illnesses ranged from 11.0% - 16.6%, and peaked during the week
of January 13, 2002. The number of respiratory outbreaks reported
each week ranged from 0 – 9, peaking during the week of January
20. When a 10% or greater increase in average respiratory ED visits
was compared to increases in respiratory outbreaks reported during
the same week, there was poor agreement (Kappa = - 0.17); however,
comparing increases in respiratory ED visits to outbreaks reported
two weeks later showed good agreement (Kappa = 0.61). One 10% increase
in respiratory ED visits was followed one week, instead of two weeks,
later by an increase in respiratory outbreaks. Reclassifying these
as a concordant pair in the analysis yielded excellent agreement
(Kappa = 0.76).
Conclusions: Information collected in Maryland
suggests that syndromic surveillance captures trends in respiratory
illnesses approximately two weeks earlier than reports of outbreaks.
This analysis indicates that in addition to serving as a system
for detecting bioterrorist events, syndromic surveillance activities
may be able to yield general illness trend information and may help
predict upcoming respiratory illnesses in the community.
Maryland Department of
Health & Mental Hygiene — Epidemiology & Disease Control
Program |
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